Interest groups have spent $1.7 million on television advertising in Wisconsin's Supreme Court race, a figure that campaign staffers expect to more than double by Tuesday's election.

A New York University study says third-party spending has dominated the TV ads aired through Tuesday in the race between Justice David Prosser and Assistant Attorney General JoAnne Kloppenburg. The Brennan Center for Justice at the university's Law School counted $769,000 from the liberal Greater Wisconsin Committee on ads attacking Prosser, compared with $415,000 from the Club for Growth and $233,000 from the Wisconsin Manufacturers & Commerce, conservative groups running pro-Prosser ads.

That data, compiled by the Campaign Media Analysis Group, likely underestimates spending, because it measures only the value of media time for ads actually aired, including those in the primary, Brennan Center counsel Adam Skaggs conceded. The figures don't include production costs, ad agency fees or future media buys, he said.

By contrast, the campaigns have compiled much higher figures, based on their contacts with television stations and media buyers.

Prosser has said he is being targeted by $3 million in attack ads. Kloppenburg's campaign said outside spending was almost evenly split: $1.9 million from the Greater Wisconsin Committee against a combined $2 million from five conservative groups: WMC, Club for Growth, Americans for Prosperity, Family Research Council Action and Citizens for a Strong America.

Ad spending frequently spikes in the week before the election, Skaggs noted. Even if the higher figures are correct, total spending would still lag behind the record-setting 2007 and 2008 campaigns, which topped $6 million each.

Few of this year's ads are coming from the campaigns. Both candidates have accepted public funding of $100,000 each for the primary and $300,000 each for the general election.

In related developments:

• A national liberal group announced it is opening a telephone bank to urge support for Kloppenburg. The Progressive Change Campaign Committee is also active in efforts to recall eight Republican state senators.

• Labor unions have donated more than twice as much to Chief Justice Shirley Abrahamson as to the other six Supreme Court justices combined, according to a study released Wednesday.

With the prospect that the high court could decide the fate of a controversial new law that eliminates most collective bargaining for most public employees, the National Institute on Money in State Politics looked at union contributions to the sitting justices from 1989 through 2009.

Abrahamson topped the list in total dollars, raising $191,163 from unions, accounting for 8% of her $2.3 million total in that period.

Prosser led the court in percentage of union donations, but only because his total fundraising was much smaller than any other justice. Unions contributed $4,500, or 15%, of the $29,940 he raised for his only previous court race. He was elected unopposed to a full term in 2001, after being appointed in 1998.